 |
|
|
|
|
 |
|
| Home | About NHGRI | Newsroom | Staff |
|
|
|
|
 |
TranscriptomeWhat is a transcriptome?A transcriptome is a collection of all the gene transcripts present in a given cell. Genes are made up of helical molecules of deoxyribonucleic acid (DNA) that contain the blueprints for making proteins. In order to actually produce proteins, these DNA blueprints must be transcribed into corresponding molecules of ribonucleic acid (RNA), referred to as messenger RNA (mRNA) or gene transcripts. The mRNA molecules then deliver the instructions for making proteins to ribosomes, which are tiny molecular "machines" found in the cytoplasm of the cell. In a process called translation, ribosomes "read" the mRNA?s sequence and produce a protein by assembling amino acid building blocks in the precise order specified by the genetic code. In addition to the thousands of genes that code for proteins, there exists a different sort of gene that is transcribed into RNA molecules but that does not code for proteins. Such gene transcripts, referred to as non-coding RNA, play roles in the structure of cell components and the regulation of DNA expression.
Is a transcriptome the same as a genome?No, a transcriptome is different from a genome, which is the entire DNA sequence of an organism. A transcriptome represents the very small percentage of the genetic code that is transcribed into RNA molecules, which is estimated to be much less than 5 percent of the genome in humans and other mammals. In addition, one of the lessons of the Human Genome Project is that each gene may produce many different types of mRNA molecules, so the transcriptome is much more complex than the genome that encodes it. What can a transcriptome tell us?The sequences of mRNAs mirror the DNA sequence of the genes from which they were transcribed. Consequently, by analyzing the transcriptome, researchers can determine when and where a gene is turned on or off in various types of cells and tissues. Depending on the technique used, it is often possible to count the number of transcripts to determine the amount of gene activity, also called expression level, in a certain cell or tissue type. The higher the number of transcripts, generally the more important that transcript is to the functioning of the cell or tissue. In humans and other multicellular organisms every cell contains the same genes, but different cells show different patterns of gene expression. These variations underlie the wide range of physical, biochemical and developmental differences seen among various cells and their respective tissues, both in health and disease. By collecting and comparing transcriptomes of different types of cells, researchers can gain a deeper understanding of what constitutes a specific cell type and how changes in cell activity may reflect or contribute to disease. Furthermore, by aligning the transcriptome of each cell type to the genome, it is possible to generate a comprehensive, genome-wide picture of what genes are active in which cells.
How can transcriptome data be used to explore gene function?Most genes do not yet have known functions. Search of a transcriptome database can give researchers a list of all the tissues in which a gene is expressed, thus giving clues to its functions. For example, if the transcriptome database shows a gene's expression levels are dramatically higher in cancer cells than in healthy cells, it is possible that the unknown gene may play a role in promoting tumor growth. Or if a gene is expressed in fat tissue, but not in bone or muscle tissue, the unknown gene may be involved in fat storage or metabolism. In both instances, having the transcriptome data gives researchers a good place to start in the search for a new gene's function. The National Human Genome Research Institute (NHGRI) is participating in two projects that will create transcriptome resources that will be made available to researchers around the world. Those projects are: the Mammalian Gene Collection and the Mouse Transcriptome Project.
What is the Mammalian Gene Collection?The Mammalian Gene Collection is a National Institutes of Health (NIH) initiative that is building a collection of copies of human, mouse and rat mRNA sequences in a form called complementary DNA (cDNA) clones. The project, which is co-led by NHGRI and the National Cancer Institute, is well over half of the way to its goal of providing at least one cDNA clone for every known human and mouse gene. Researchers can view the cDNA sequence data in a free, public database located at the Mammalian Gene Collection [mgc.nci.nih.gov]. They can also order copies of these cDNA clones and then insert them into bacterial or mammalian cells, causing the cells to synthesize the proteins encoded by that particular gene transcript. This enables researchers to study the protein's properties in greater detail, as well as to examine the effects that the protein and mutant versions of the protein may have on various cell types.
What is the Mouse Transcriptome Project?The Mouse Transcriptome Project is an NIH initiative that is generating a free, public database of gene transcripts for many mouse tissues. Currently, transcriptome data are available on more than 90 tissue samples. These tissue-specific expression data, which are mapped to the mouse genome, are available in a searchable format in the Mouse Reference Transcriptome Database [ncbi.nlm.nih.gov] and at the Mouse Reference Transcriptome [sgbpub.lynxgen.com]. The mouse was chosen for this effort because its genome has been sequenced, because its tissues can be obtained under rigorous quality control conditions, and because of its importance as a model for the study of human biology and disease.
What is the role of the National Human Genome Research Institute (NHGRI) in the Mouse Transcriptome Project?NHGRI is one of 14 NIH institutes that is supporting the project with funding and scientific leadership. Other participating institutes are: National Cancer Institute, National Center for Biotechnology Information, National Institute on Aging, National Institute of Child Health and Human Development, National Institute on Deafness and Other Communication Disorders, National Institute of Dental and Craniofacial Research, National Institute on Drug Abuse, National Institute of Diabetes and Digestive and Kidney Diseases, National Institute of Environmental Health Sciences, National Institute of General Medical Sciences National Heart, Lung, and Blood Institute, National Insitute of Mental Heath, and National Institute of Neurological Disorders and Stroke.
Last Reviewed: December 2, 2008 |
|
|
|
||||||||||||||||||||||||||||||||
|
Privacy CopyrightContactAccessibilitySite MapStaff DirectoryFOIAHome |
   |
|
Print Version
